The mechanical environment profoundly influences the structure and function of the lung, from branching morphogenesis and cellular differentiation in the developing lung, to growth, injury, and remodeling of the mature organ. The underlying molecular mechanisms by which cells sense and respond to their mechanical environment remain elusive. Recently obtained evidence demonstrates that the intercellular spaces separating airway epithelial cells are highly deformable under physiological loads. These intercellular spaces are the site of putative autocrine signaling loops involving the epidermal growth factor receptor (EGFR) and its ligands. Physiological levels of mechanical stress applied to airway epithelial cells, both in vitro and in situ, trigger signaling through the EGFR pathway. Integration of these observations leads to the following central hypothesis: mechanical stress can be transduced through the steady-state activity of an autocrine EGFR loop operating in a dynamically regulated intercellular space. This hypothesis will be tested in the following three specific aims using primary human airway epithelial cultures: (1) establish the molecular components and constitutive functionality of the autocrine signaling loop in the epithelial intercellular space; (2) define the dynamic biophysical response of the intercellular space to physiologically relevant loading conditions; and (3) use biochemical and computational tools to test the central hypothesis, then explore its biological role in modulating the expression of mucSAC, a marker of the mucus secretory phenotype upregulated in various airway disorders. The resulting insights could establish a new and unanticipated paradigm for mechanotransduction occurring in the extracellular space, and change our view of how mechanical forces contribute to the biology of the airways in health and disease. The lung experiences a range of mechanical forces during normal (e.g breathing) and disease (e.g. asthma) conditions, influencing lung structure and function. The proposed studies will explore how the cells that line the airways sense and respond to changes in their mechanical environment. These studies will provide a framework for understanding and modulating mechanical responses in the lung.